Audiometry

Question 1

How can the speed of sound waves be calculated?

Answer 1

product of wavelength and frequency

c = λ * f

Question 2

What is acoustic impedance?

How is it calculated?

Answer 2

resistance type of quantity, characterizing the sound conducting medium
Z = c * ρ

• c = velocity of sound in the medium
• ρ = density of the medium

Question 3

2 formulas to describe sound intensity.

Answer 3

average power of sound (P) incident perpendicular to a surface divided by the surface area (A)
J = P / A

or: square of the effective value of the pressure (p_eff) divided by the acoustic impedance (Z)
* *J = p_eff² / Z**

Question 4

What is the the coefficient of reflection?

Formula.

Answer 4

percentage of reflected intensity

R = J_refl / J₀ = ((Z₁ - Z₂) / (Z₁ + Z₂))^2​

Question 5

What is the characteristic frequency of the reference sound?

Answer 5

1000 Hz

Question 6

What is the reference intensity?

Answer 6

intensity of the threshold of hearing at 1000 Hz (= reference sound)

J₀ = 10^-12 W/m²

Question 7

What are Fourier analysis and harmonic synthesis?

Answer 7

Fourier analysis:

decomposition of a waveform (sound) into the series of harmonics of determined

• frequencies
• amplitudes
• phase

Harmonic synthesis = reverse process of Fourier analysis

reconstruction of any periodic waveform from its harmonic components

Question 8

Was is pitch?

How can you calculate it?

Answer 8

physiological sensation of the highness or lowness of the note
⇒ that is a logarithmic function of frequency (valid up to 1 kHz): n_octave = log₂ f₂/f₁

Question 9

What is timbre?

Answer 9

determined by the amplitudes of the fundamental frequency and harmonics in the Fourier analysis of the waveform

• pure sine wave
• music
• noise
• transient

Question 10

Give 2 formulas to calculate the intensity level.

Answer 10

logarithm of the intensity ratio
J_dB = 10 lg (J₁ / J₂)

J_dB = 10 lg (J / J₀)

⇒ measured in dB

Question 11

What is the loudness level?

It was introduced by.. ?

In which unit is it measured?

By how much do we have to increase it in order to achieve a 2 times louder sound senation

Answer 11

sound of different frequency appears at same loudness level at different intensities (cf. blue curves)
→introduced by Weber-Fechner

L_phon = J_{dB 1000 Hz} = 10 lg (J / J₀)_{1000 Hz}

Phon value of any frequency = dB value of the reference sound (1000 Hz, sin)

• ex: 90 phon = 90 dB at 1000 Hz
• BUT: +10 phon = +10 dB (at 1000 Hz) = 2 times louder sound sensation

Question 12

What is the loudness?

In which unit is it measured?

1 [unit] refers to which intensity level?

What is the formula to convert it to dB?

By how much do we have to increase it in order to achieve a 2 times louder sound senation

Answer 12

psychophysical quantity, its value represents how loud we feel a sound of given intensity
→ derivation of Steven’s law:

L_son = 1/16 (J / J₀)^0.3

• 1 sone = 40 phon
• BUT: +1 sone = +10 phon = 2 times louder sound sensation

Question 13

What is the threshold of hearing?

Answer 13

smallest intensity of sound at a given frequency that human ear can just hear (approx. 10^-12 W/m²)

Question 14

What is the threshold for pain?

Intensity?

Answer 14

highest intensity of sound that one can tolerate for a short time without any harm (approx. 10 W/m^{<strong>2</strong>})

Question 15

What do the blue lines on the equal loudness curve plot resemble?

Conclusions?

Answer 15

equal loudness curves = isophon curves ⇒ same sensed loudness at different frequencies

conclusions:

• the lower the sound (frequency), the higher the intensity (dB) to hear a sound of the same loudness
• threshold of hearing = 0 phon
• threshold of pain = 130 phon
• • 10 phon = + 10 dB (at 1000 Hz)
    + 1 sone = + 10 phon

Question 16

Which quantities are brought into relation in Steven’s law?

Formula.

Answer 16

relationship btw the stimulus and sensation (valid for every sensory process)

S = const (J / J0)ⁿ

• S = power of sensation
• n = exponent corresponding to part. sens. proc.

Question 17

Relate Steven’s and Weber-Fechner’s law in a graph.

Answer 17

Question 18

What is the minimum time for a sound stimulus?

Answer 18

0.2 s, for tests at least 1.0 s

Question 19

What is responsible for additional hearing loss?

How is it measured?

When do we speak of impaired hearing?

Answer 19

over a certain loudness level the impairment is proportional to the received dose of the sound ⇒ causes hearing loss
D = J * t

• D = dose
• J = intensity
• t = time

→ impaired if hearing loss of - 30 dB

Question 20

How is audiometry done?

Answer 20

1. Recording the threshold of hearing as a function of frequency
2. compared to the normal value of the threshold of hearing at given frequency → difference in [dB] = hearing loss
3. audiogram can be constructed

Question 21

What is an audiogram?

Draw it.

Answer 21

hearing loss (dB) vs. frequency plot

Question 22

What is a pure-tone audiometer?

Differentiate.

What is it used for?

Answer 22

device that generates output of harmonic (sinusoidal) voltage of adjustable frequencies to air/bone conduction headphones

• air conduction: normal headphones, entire ear tested
• bone conduction: bone vibrator attached to mastoid bone, middle ear does not participate → less sensitive by 40 - 60 dB

⇒ difference btw 2 audiograms indicates injuries of middle ear

Question 23

How is normal hearing loss called?

At what age does it usually start?

Answer 23

presbyscusia = usually - 3dB

starts at 20

Answer 24

NOCH AUSSTEHEND!